i SUCCESS OF SHORT- VERSUS LONG- DENTAL IMPLANTS IN THE BICUSPID AREA: A RETROSPECTIVE STUDY by Eyad Al-Khalifa D.M.D., University of Pittsburgh, 2002 M.D.S., University of Pittsburgh, 2013 Submitted to the Graduate Faculty of the School of Dental Medicine in partial fulfillment of the requirements for the degree of Master of Science in Dental Medicine University of Pittsburgh 2013
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i
SUCCESS OF SHORT- VERSUS LONG- DENTAL IMPLANTS IN THE BICUSPID AREA: A RETROSPECTIVE STUDY
by
Eyad Al-Khalifa
D.M.D., University of Pittsburgh, 2002
M.D.S., University of Pittsburgh, 2013
Submitted to the Graduate Faculty of
the School of Dental Medicine in partial fulfillment
of the requirements for the degree of
Master of Science in Dental Medicine
University of Pittsburgh
2013
ii
UNIVERSITY OF PITTSBURGH
SCHOOL OF DENTAL MEDICINE
This thesis was presented
by
Eyad Al-Khalifa D.M.D.
It was defended on
May 28, 2013
and approved by
Committee Member: Ali Seyedain DMD, MDS, Assistant Professor. Director of the Undergraduate Clinic.
Department of Periodontics and Preventive Dentistry
Committee Member: Anitha Potluri DMD, Assistant Professor. Department of Oral Radiology
Committee Member: Richard A. Bilonick PhD, Assistant Professor. Department of Ophthalmology, School of
Medicine; Department of Orthodontics, School of Dental Medicine; Department of Biostatistics, Graduate
School of Public Health
Thesis Advisor: Pouran Famili DMD, MDS, MPH, PhD, Professor and Chair. Director of the Residency
Program. Department of Periodontics and Preventive Dentistry
Mixed effect model predictions for the square root of mean bone loss as a function of implant
diameter ……………………………………………………………….……………………....45
Figure 10.
Failure plots for age, implant length and implant diameter……………………………….……..46
x
PREFACE
The author would like to express profound gratitude to his advisor, Dr. Pouran Famili,
for her invaluable support and continuous guidance which enabled him to complete his work
successfully. Author is highly thankful to Dr. Richard A. Bilonick, for his supervision and
statistical analysis for this research work. It is a pleasure to the author to thank Dr. Ali
Seyedain and Dr. Anitha Potluri for giving him thoughtful academic advice as a committee
member for the thesis.
The author is indebted to his mother for her love, prayer and support throughout his
life. Nothing one can say can do justice to how he feels about her support. Special thanks go
to his two daughters, Acacia and Basma for their love.
Last but by no means least; it gives the author immense pleasure to thank his wife
Aseel. His wife is his source of strength and energy. Without her support, this thesis would
never have started, much less finished.
1
1.0 INTRODUCTION
The osseointegrated implant has been thoroughly investigated and its use reported in more
than 1,000 published papers based on various animal and human models. Criteria for the
evaluation of dental implant success are proposed. These criteria are applied in an
assessment of the long-term efficacy of dental implants in current use, including short dental
implants. Anatomical limitations very often represent a contraindication to implant therapy.
After tooth loss, however, severely atrophic residual alveolar ridges are quite common,
especially in patients who have been edentulous for a long period of time. Reduced alveolar
bone height in posterior areas of the maxilla and mandible propose a great challenge for
dentists and dental specialists who use implant therapy to replace a missing tooth, unless a
procedure such as ridge augmentation or sinus floor elevation is performed. Although widely
utilized, these techniques imply greater morbidity, longer treatment times and higher costs.
The sinus cavity intruding into the maxilla and the close proximity of the alveolar nerve in the
mandible are clinical situations where short implants may be considered a successful
alternative treatment option.
This research is a retrospective review of existing medical records utilizing the
University of Pittsburgh School of Dental Medicine Electronic Health Record, stored in its
axiUm database [Exan® Las Vegas NV].
2
1.1 REVIEW OF THE LITERATURE: DENTAL IMPLANT
1.1.1 History of the dental implant
Early civilizations recognized the benefit of tooth replacement with different kinds of implants.
The Mayan civilization has been shown to have used the earliest known examples of dental
implants. Archaeologists have found a fragment of mandible of Mayan origin, dating from
about 600 AD. This mandible, considered to be a woman in her twenties, had three tooth-
shaped pieces of shell placed into the sockets of three missing lower incisor teeth. The idea
of the subperiosteal implant was first proposed by Dahl in 1941 in Sweden, and was later
patented by him in the USA in 1942. After various modifications by prominent clinicians such
as Gershkoff, Goldberg, Linkow, Cranin, and more recently by Robert James (at Loma
Linda), today the modern subperiosteal implant modality is used routinely, mainly in the
United States, with very high success rates (90+ % over five years) and predictability
matched only by the root-form implants. The modern subperiosteal implant modality was
recognized by the National Institutes of Health (NIH) in 1988 as a major implant modality for
the treatment of atrophied jaws. Golec et al. (1992) has shown that coating subperiosteal
implants with hydroxyapatite may result in direct bone interface (a phenomenon called
"biointegration" of HA) rather than attachment by a suspensory ligament. In 1952, in a
modestly appointed laboratory in the university town of Lund, Sweden, Professor Per-Ingvar
Brånemark had a lucky accident, or what most scientists would call serendipity. Much to his
irritation, Dr. Brånemark discovered that it was impossible to recover any of the bone-
anchored titanium microscopes he was using in his research. The titanium had apparently
3
bonded irreversibly to living bone tissue, an observation which contradicted contemporary
scientific theory. Dr. Brånemark subsequently demonstrated that under carefully controlled
conditions titanium could be structurally integrated into living bone with a very high degree of
predictability and without long-term soft-tissue inflammation or ultimate fixture rejection.
Brånemark named the phenomenon osseointegration. The first practical application of
osseointegration was the implantation of new titanium roots in an edentulous patient in 1965.
More than thirty years later, the non-removable teeth attached to these roots are still in
function.
1.1.2. Types of dental implants
The dental implant is a prosthetic device of allopastic material implanted into the oral tissues
beneath the mucosa and/or periosteal layer, and/or within the bone to provide retention and
support for a fixed or removable prosthesis.
1.1.2.1 Subperiosteal implants Subperiosteal implants were already introduced by
Dahl in 1943. Of all currently-used devices, the subperiosteal implant has had the longest
period of clinical trial. No specific animal research programs with subperiosteal implants
appear to have been undertaken in the past decade. As shown below in Figure 1, these
subperiosteal implants are not anchored inside the bone as endosseous devices, but are
instead shaped to "ride on" the residual bony ridge. They are not claimed to be
4
osseointegrated (Bodine 1980). The optimal outcome of subperiosteal implant therapy is
represented by the long-term material of Bodine and Yanase (1959) whose ten-year report
indicated success in the range of 66% ± 8%.
Figure 1. Subperiosteal Implant Source: Taylor, Thomas D. Laney, William R. (1993). Dental Implants: Are They for Me? (Educate Your Patients). London: Quintessence. Reprinted with permission from Dr. Taylor, 05-03-2013
1.1.2.2 The Transosteal, mandibular staple bone plate
Small and Kobernick (1969) inserted stainless steel threaded pins shown in Figure 2 that
pass through the mandibles of edentulous dogs, and described tissue reactions over a
period up to 12 months. Small 1985 presented some post-mortem evidence of
5
osseointegration of the surgical implant screws, particularly in one case that was examined
six years after insertion. Mandibular staple implants are indicated for insertion in the
edentulous mandible with a minimal alveolar ridge height of 8 to 9 mm (Small 1985). In 1980
Small published a review of 1,516 cases, with rates of cumulative success at 94.6% for five
to six years and 90.9% for 8 to 16 years. A total 395 among the 1,516 cases had retained the
staples five years or longer. Gingival hyperplasia and/or infection about one or both
transosteal pins was reported to be a complication in 10% to 15% of cases. Bone loss in 30
cases in the long-term follow-up (5 to 14 years, mean nine years) averaged only 0.78 mm.
Figure 2. Transosteal Implant Source: Taylor, Thomas D. Laney, William R. (1993). Dental Implants: Are They for Me? (Educate Your Patients). London: Quintessence. Reprinted with permission from Dr. Taylor, 05-03-2013
6
1.1.2.3 The endosseous implants The use of commercially pure titanium as an
implant material was documented by Brånemark in 1977. His discovery of the
osseointegrated implant led to the development of root-form endosseous dental implants as
shown in Figure 3. They have become the standard in dentistry in the last 20 years.
According to the FDA report Class II Special Controls Guidance Document: Root-form
Endosseous Dental Implants and Endosseous Dental Abutments, “the root-form endosseous
dental implant device refers to the fixture that is surgically implanted into the patient’s bone.
The root-form endosseous dental implant device is intended to be surgically placed in the
bone of the upper or lower jaw arches to provide support for prosthetic devices, such as an
artificial tooth, in order to restore the patient’s mastication function.”
Figure 3. Endosseous Implant Source: Taylor, Thomas D. Laney, William R. (1993). Dental Implants: Are They for Me? (Educate Your Patients). London: Quintessence. Reprinted with permission from Dr. Taylor, 05-03-2013
7
In 1981 Adell reported the success rate of 895 implant fixtures over an observational period
of five to nine years after placement. Eighty-one percent of maxillary and 91% of mandibular
implants remained stable. Brånemark and Albrektsson (1986) evaluated the outcome of all
implants inserted during one year and then followed up for five years and found an implant
success rate of 96.5% in the mandible. The great majority of all published papers have
reported a positive outcome of endosseous implants in 90% to 100% of the cases.
1.1.3 Implant–tissue interface
1.1.3.1 Implant-soft tissue interface The implant-soft tissue interface is similar to
that present in the natural dentition, as seen in Table 1, with a functional junctional
epithelium containing basal lamina and hemidesmosomal attachments (Gould 1981,1984).
TABLE1
Characteristics of the soft tissue interface
Feature Tooth Implant
Sulcular epithelium + +
Junction epithelium + +
Basal lamina + +
Hemidesmosomes + +
Glycoprotein adhesion + +
Connective tissue fiber insertion + -
*Table 1 adapted from G.R. Bauman et al.(1993) The Peri-Implant Sulcus. International Journal of Oral and Maxillofacial Implants 8(3):273-280. Reprinted with permission from the journal, 05-03-2013
Meffert (1988) presented evidence supporting the concept that a viable biologic seal can
exist between the epithelial cells and the implant. Kurashina 1984 described non-inflamed
8
and inflamed peri-sulcular tissue at 27 dense hydroxyapatite (HA) implants in dogs, which
closely parallels that observed about natural teeth in the same animal model:
1. Non-inflamed: In the connective tissue of the gingiva, a limited infiltration of
inflammatory cells was noted. This field of inflammatory cells was the same area as
that in the gingiva of neighboring teeth. Outside this area, numerous bundles of
collagen fibers were seen and many of these fibers terminated perpendicularly to the
interface with the implants, resulting in a saw-toothed pattern (Sharpey's fibers?). The
epithelium on a lower level, adjoining the implant surface, was 2 to 5 cells thick. There
was no cell differentiation between the subsequent superficial layers, no
keratinization, and few or no papillae.
2. Inflamed: There were multiple bone resorptions at the alveolar bone crest. In some
sections, islands of bone were seen lying at the interface with the implant, just above
the alveolar bone. At the supra-alveolar level the gingival connective tissue showed a
large field of inflammatory cells and disappearance of collagen fibers. Epithelial
downgrowth lined the implant sulcus. The lowest level was always above the alveolar
bone.
The most critical difference between periodontal and peri-implant tissue is the absence of
Sharpey's fibers extending into the implant. Collagen fibers are non-attached and run parallel
to the implant surface owing to the lack of cementum (Samachiaro 1986, Fukuyama 1986).
However some reports have suggested that microscopic irregularities and porosities, such as
would be found on plasma-sprayed titanium surfaces, may favor the appearance of fibers
oriented perpendicularly to the implant surface (Buser 1992, Schroeder 1988).
9
1.1.3.2 The implant-bone tissue interface The relationship between endosseous
implants and bone consists of one of two mechanisms: osseointegration, when the bone is in
intimate contact with the implant, or fibro-osseous integration, in which soft tissues, such as
fibers and/or cells, are interposed between the two surfaces. Brånemark et al. (1969)
proposed the concept of osseointegration; the related concept functional ankylosis by
Schroeder (1988) states that there is an absence of connective tissue or any non-bone
tissue in the interface between the implant and the bone. Osseointegration refers to the
direct contact of bone and implant at the light-microscope level. Sections viewed with
electron microscopy have revealed a proteoglycan layer (containing calcified tissue) in direct
contact with the titanium oxide surface implant. The proteoglycan layer is 40 to 200 Å thick
(Albrektsson 1985). Meffert et al. (1987) suggested that only hydroxyapatite, and not
titanium, was capable of true bonding to bone. Bagambisa et al. (1990) reported that an even
carpet of multilayered osteoblasts covered the surface of HA implants, with bone infiltrating
the porous surface. Hydroxyapatite was not osteoinductive but acts as a nucleation site for
osteoid material. Bone formation occurred through epitaxial crystal growth.
1.2 IMPLANT PLACEMENT CONCERNS
Dental implant placement is no longer performed only by oral surgeons and periodontists;
general dentists are also increasingly providing difficult surgical implant services. Dental
implants may be used to replace single teeth, replace multiple teeth, or provide abutments
for complete dentures or partials. It is essential to obtain appropriate information about the
10
oral vital structures prior to implant placement. Knowledge of anatomy and its variations is
essential to ensure precise surgical procedures to safeguard the patient’s vital structures
(Greenstein 2008).
1.2.1 Anatomic concerns
Prior to commencement of implant surgery, careful and detailed planning is required to
identify maxillary and mandibular vital structures as well as the shape and dimensions of the
bone, so the implants can be properly oriented and placed. During the planning phase of
treatment, the recipient bed is routinely assessed by visual examination and palpation, as
well as the available medical imaging modalities. When adequate occlusoapical bone height
is available for endosteal implants, the buccolingual width and height of the available bone
are the most important criteria for implant selection and success.
1.2.1.1 Quality and Quantity of alveolar bone Lekhom and Zarb (1985) classified
the volume of remaining mineralized bone at the edentulous sites into five different groups
based on shape, and the “quality” of the bone in the edentulous site into four types. (Please
see Figure 4).
11
Figure 4. Classifcation of residual jaw shape and jaw bone quality
Source: Ulf Lekholm. Surgical considerations. Journal of Prosthetic Dentistry 79(1):43-48, 1998. Reprinted with permission from the journal, 05-03-2013
(Detail for Figure 4):
Shape Groups A-E
A. Virtually intact alveolar ridge
B. Minor resorption of the alveolar ridge
C. Advanced resorption of alveolar ridge to the base of the dental arch
D. Initial resorption of the base of the dental arch
E. Extreme resorption of the base of the dental arch.
12
Quality Groups 1-4
1. Almost the entire jaw is composed of homogenous compact bone.
2. A thick layer of compact bone surrounds a core of dense trabecular bone.
3. A thin layer of compact bone surrounds a core of dense trabecular bone of favorable
strength.
4. A thin layer of cortical bone surrounds a core of low density trabecular bone.
Bone quality types 2 and 3 are found much more frequently than types 1 and 4. Although
variation in density exists in each region, quality 2 dominates the mandible and quality 3
bone is more prevalent in the maxilla (Truhlar 1997).
13
1.2.1.2 Mandibular canal The mandibular canal is one of the most important
anatomical structures in the mandible, because it carries the inferior alveolar neurovascular
bundle: the inferior alveolar nerve (IAN) and the inferior alveolar artery, vein, and lymphatic
vessels (Tammisalo 1992). Rajchel (1986), studying 45 Asian adults, demonstrated that the
mandibular canal, when proximal to the third molar region, is usually a single large structure
2.0 to 2.4 mm in diameter. Clinicians should be aware of variation in the course of the
mandibular canal as it runs through the jaw, because the mandibular canal may present in
different anatomical configurations in the vertical plane. According to Anderson (1991) the
canal may run lower when it proceeds anteriorly, or may present a sharp decline, or drape
downward in catenary fashion. Nortje et al. (1977), on panoramic radiographs, showed that
the vertical mandibular canal position can be divided into four categories: 1) high mandibular
canal (within 2 mm of the apices of the first and second molars); 2) intermediate mandibular
canal; 3) low mandibular canal; and 4) other variations – these include duplication or division
of the canal, apparent partial or complete absence of the canal or lack of symmetry.
According to Gowgiel (1992), the neurovascular bundle from the mandibular foramen to the
mental foramen is always in contact with, or in close proximity to, the lingual mandibular
cortex. It has been shown that vascular and nerve bundles may be extremely close to the
buccal cortex of the mandible in patients with broad and thick mandibular rami. Dario (2002)
suggested that clinicians should consider obtaining a preoperative tomogram to avoid nerve
injuries prior to implant placement above the inferior alveolar canal (Greenstein and Tarnow
14
2006, from Dario 2002). A mean incidence of neurosensory disturbance incidence after
implant surgery was 6.1% (Goodacre 1999) to 7% (Goodacre 2003), with a range between
0.6% and 39%.
1.2.1.3 Mental nerve and it’s anterior loop One of the most challenging regions to
do implant placement in mandible is the area of the mental foramen region. This is because
there are many variations with regard to the size, shape, location and direction of the
opening of the mental foramen. The shape of the mental foramen can be round or oval:
diameter ranges from 2.5 to 5.5 mm (Neiva 2004; Apinhasmit 2006; Yosue 1989). The
position of the mental foramen was recorded as either in line with the longitudinal axis of a
tooth or as lying between the two teeth. The mental nerve is at particular risk of iatrogenic
injury because it arises from the asymmetric foramina and forms a concave loop anteriorly.
In edentulous patients, the mental nerve may be very close to the bone surface or the top of
the crest. Nerve injury may cause parasthesia (numb feeling), hypoesthesia (reduced
feeling), hyperesthesia (increased sensitivity), dysthesia (painful sensation), or anesthesia
(complete loss of feeling) of the teeth, the lower lip, or the surrounding skin and mucosa
(Greenstein and Tarnow 2006, from Sharawy and Misch 1999). Bavitz (1993) measured
anatomically and radiographically the anterior loop of the mental nerve in twenty-four
cadavers (please see Table 2).
15
TABLE 2
Measurement of the anterior loop from the mental foramen
Anatomic measurement Radiographic
measurement
Dentate Average 0.2 mm
Range 0 -1 mm
Average 2.5 mm
Range 0 – 7.5 mm
Edentulous Average 0.0 mm Average 0.6 mm
Range 0 – 2 mm
*Table 2 adapted from Bavitz JB. An anatomical study of mental neurovascular bundle-implant relationships. International Journal of Oral and Maxillofacial Implants 8(5):563-567, 1993. Reprinted with permission from
the journal, 05-03-2013
The most anterior position in which the mental nerve is commonly found is 1 mm forward or
mesial to the most anterior aspect of the mental foramen (Bavitz 1993). Based upon Bavitz’
finding, implants can be placed as close as one millimeter anterior to the radiographic mental
foramen. Over-penetration occurs when the cortical portion of the alveolar crest places
resistance on the drill. However, as it enters the marrow spaces, a drill may drop into the
neurovascular bundle unless the surgeon has excellent control (Misch and Wang 2008). A
safety margin of 2mm between the entire implant body and any nerve canal should be
maintained (Greenstein 2008, from Greenstein and Tarnow 2006; Worthington 2004).
16
1.2.1.4 Vasculature in the floor of the mouth The arterial blood supply of the floor
of the mouth is formed by an anastomosis of the sublingual and submental arteries. The
submental artery (2mm average diameter) (Hofschneider 1999) is a branch of the facial
artery. The sublingual artery (2 mm average diameter) arises from the lingual artery and is
found coronal to the mylohyoid muscle (Martin 1993). Intraosseous hemorrhage is not a
serious event, and control of the hemorrhage can be ensured by compressing the area with
a directional indicator, an abutment, or the implant. A vascular wound may occur after
detrimental surgical manipulations or tearing of the lingual periosteum, but in most cases it is
attributed to perforations of the lingual cortical plate. Mechanical pressure exerted by the
expanding hematomas displaces the tongue and floor of the mouth both superiorly and
posteriorly (Kalpidis and Setayesh 2004). This occurrence may lead to extensive bleeding
into the submandibular space, resulting in a life-threatening acute airway obstruction within
the first few hours after surgery (Goodacre 1999).
1.2.1.5 Maxillary sinus The maxillary sinus is the largest paranasal sinus. It is
pyramidal in shape. The base of the sinus lies vertically on the medial surface of the lateral
nasal wall. The average volume of a fully developed sinus is about 15ml but may range
between 4.5 and 35.2ml. The Schneiderian membrane, which lines the sinus, is adherent to
underlying bone. The structures beneath the sinus consist of the alveolar ridge and maxillary
posterior teeth (Small 1993). One or more septa, also referred to as Underwood’s septa,
divide the floor of the maxillary sinus into several recesses and may thus cause various
17
complications during sinus-lift procedures. The overall prevalence of one or more sinus septa
is between 26.5% and 31% (UIm 1995; Kim 2006) and is most common in the area between
the second premolar and first molar.
It is well known that the sinus expands with age, and especially when posterior teeth
are lost. The sinus cavity expands both inferiorly and laterally, potentially invading the canine
region. This phenomenon is called pneumatization of the sinus. This finding is related to two
phenomena:
1) The enlargement of the sinus at the expense of the alveolus after tooth extraction
because of the increased osteoclastic activity of the periosteum of the Schneiderian
membrane (Kraut 1989).
2) Increased pneumatization of the sinus because of the increase in positive intra-antral
pressure (Smiller 1992).
The poor bone quality and inadequate bone volume in the posterior maxilla often presents
specific problems for the placement of dental implants. To increase the amount of bone in
the posterior maxilla, the sinus lift procedure (subantral augmentation) was developed in the
mid-1970s (Linkow 1966). The sinus lift is a well-accepted technique to treat the loss of
vertical bone height (VBH) in the posterior maxilla performed in one of two ways, either via a
lateral window technique or (Summers 1994) by an osteotome sinus floor elevation
technique with bone-graft material placed in the maxillary sinus to increase the height and
width of the available bone. [Table 3. contains a guideline for sinus floor elevation.]
18
TABLE 3
General Guidelines for Sinus Floor Elevation
Vertical Bone Height Surgical Procedure Implant Placement
>/= 10 mm None needed Immediate
7 mm to 10 mm Sinus floor elevation via
osteotome technique
Immediate
5 mm to and 7 mm Sinus floor elevation via
lateral window approach
Immediate
1 mm to 4 mm Sinus floor elevation via
lateral window approach
Delayed
*Table 3 adapted from Georglos Tasoulis (2011), The Maxillary Sinus: Challenges and Treatments for Implant Placement. Compendium 32(1):10-20. Reprinted with permission from the journal, 05-03-2013
The most common intraoperative complication seems to be Schneiderian membrane
perforation, occurring in 10-60% of all procedures (Ardekian 2006; Pikos 1999). The
Schneiderian membrane could present a window for bacterial penetration and invasion into
the grafted area (Zijderveld 2008). Failure to atraumatically elevate the Schneiderian
membrane may result in graft migration or loss, exposure of the graft or implant to the sinus,
and postoperative site infection. In addition to contaminating the recipient site, disruption of
the mucosa may alter the normal mucociliary flow patterns, causing retention of secretions
and infections around the foreign body (Ward 2008).
19
1.3 ROLE OF RADIOGRAPHIC EVALUATION IN DENTAL IMPLANT
PLACEMENT
In dental practice, imaging is recommended for preoperative evaluation of the implant site,
and postoperatively for the evaluation of correct seating of the abutment and further
evaluation of bone loss under an implant maintenance regime. Radiography plays a vital role
in diagnosis and treatment planning to place the implant.
Before attempting to treat a patient with an endosseous dental implant, dentists must
determine jaw size, boundaries, and orientation of the vertical long axis of the jaw. In
addition, internal anatomy should be visualized in three-dimensional perspectives, including
the proximity of nasal fossae, neurovascular bundles, pneumatization of the maxillary sinus,
soft tissue morphology, and bone quality. Imaging information will allow optimum placement
of the implants and enhance the success, both short- and long-term, of all subsequent
stages of the procedure.
1.3.1 Imaging modalities
The American Academy of Oral and Maxillofacial Radiology (AAOMR) (White 2001) has
described the selection criteria for dental implant imaging. To assess the suitability of an
implant site, the clinician must be able to visualize the mesial–distal view of the region of the
arch where implant placement is being considered.
In many practices, digital radiographs have largely replaced conventional films. As a
result, many dentists will find they are already familiar with the combination of rapid imaging
and computer display that cone-beam units provide. Digital images will not fade and can be
20
stored on a computer along with other patient information. They can be manipulated easily
on a computer, where angles can be rotated, grayscale intensities can be adjusted, negative
and positive can be reversed, and pseudo-color can be added to enhance contrast to
facilitate immediate diagnosis. These are all major advances over trying to make a diagnosis
by examining films by hand.
1.3.1.1 2-D imaging: periapical and panoramic radiography
Periapical radiographs are images of a limited region of the mandibular or maxillary alveolus.
Periapical radiographs are produced by placing the film intra-orally parallel to the body of the
alveolus with the central beam of the X-ray device perpendicular to the alveolus at the region
of interest, producing a lateral view of the alveolus. Unscreened radiographs provide high-
resolution (more than 20 line pairs per mm) and sharp images, which allow accurate
measurements in the horizontal direction, specifically measuring the proximity of adjacent
tooth roots. These are well-suited for documentation and assessment of possible peri-
implant bone resorption during follow-up and are considered superior to panoramic
radiography in this respect (Strid 1985). With proper positioning techniques, periapical
radiographs give minimum magnification and distortion and the reproducibility of these
radiographs is high.
Panoramic radiography is a curved plane tomographic radiographic technique used to
depict the body of the mandible, maxilla, and the lower one-half of the maxillary sinuses in a
single image. Panoramic radiography allows complete visualization of the relationship of the
maxillofacial structures within the focal trough, and provides information on the relative
21
position of the inferior alveolar canal and the maxillary sinuses in relation to the crest of the
alveolar ridge. It provides an approximation of bone height and vital structures and any
pathological conditions that may be present (Strid 1985). The major disadvantages of
panoramic radiography are an unpredictable distortion of the visualized structures and a low
level of reproducibility.
Two-dimensional images cannot provide clinicians with information about the
buccolingual cross-sectional dimension or the inclination of the alveolar ridge (Fredholm
at osteotomy; dis.plac=Distal distance shoulder implant/crestal bone at osteotomy; meanplac= Mean distance at osteotomy;
mes.crwn= Mesial distance shoulder implant/crestal bone with crown; dis.crwn=Distal distance shoulder implant/crestal bone with
crown; meancrwn= Mean distance with crown; mes.boneloss= Mesial Bone loss; dis.boneloss= Distal Bone loss; mean.boneloss=
Average Bone loss; sqrt.mbl= Square-root average bone loss; sqrt.mes.mbl= Square-root mesial bone loss; sqrt.dis.mbl= Square-root
distal bone loss.
44
FIGURE 8 Mixed effect model predictions for the square root of mean bone loss as a function of implant length (implant diameter equal to its mean value).
45
FIGURE 9 Mixed effect model predictions for the square root of mean bone loss as a function of implant diameter (implant length equal to its mean value).
46
FIGURE 10 Failure plots for age, implant length and implant diameter. Smoothing spline probability predictions are denoted by red lines. Log-binomial mixed effects model predictions are denoted by green lines. Due to the small number of levels for implant diameter, it was not possible to compute the smoothing spline predictions.
47
3.0 DISCUSSION
Criteria for successful integration of dental implants have been proposed (Albrektsson
1986). Of these, a lack of mobility is of prime importance as ‘loosening’ is the most
often-cited reason for implant fixture removal. Adell (1981) reported success rates for
895 implant fixtures over an observational period five to nine years after placement.
Eighty-one percent of maxillary and 91% of mandibular implants remained stable.
The results of this study showed that failures appear to relate somewhat with
age, length, and diameter. Plots illustrating the excellent model fit for each subject are
shown in Figures 8 and 9. Because the model was fitted to the square root transformed
bone loss, Tables 7 and 8 were constructed to help show how mean bone loss is
expected to change over the ranges of implant diameter and length, respectively, based
on the estimated fixed effects. As shown in Table 7, as diameter increased, mean bone
loss was expected to decrease from 1.15m to 0.86mm as the diameter goes from
3.5mm to 5mm. This negligible change was not statistically significant, although even if
they were real, the estimated effects were small. As can be seen in Table 8, mean bone
loss is expected to increase from 1.046 mm to 1.054 mm as implant length increases from 8
mm to 16 mm. Again, this change is not statistically significant. Even if it is real, the amount
of change is likely to be negligible if the point estimate is accurate. However, all failure
implants occurred before prosthesis connection, with similar results reported in
Goodacre (2003). It is likely that bone quality and suitable surgical protocols play a
more major role in short-implant prognosis than prosthetic features. The relative risk for
this study regarding length was not significant (p = 0.57) and was comparable to results
48
from clinical studies of short-length implants (Tawil 2003; Renouard 2003). It supports
the hypothesis that short implants (8-10mm) might give similar long-term implant
survival rates to longer implants used in larger bone volumes.
Das Nerves (2006) reviewed the results of 33 studies of 16,344 Brånemark-type
implants, and assessed failure rates over time. Seven-hundred-eighty-six failures were
reported, representing a failure rate of 4.8%. He also showed no correlation between
implant length and implant success or failure, except in a single instance where
machined-surfaced, hex-headed, countersunk implants were placed in poor-quality
bone.
The results of this study showed five implant failures (Table 9b), with a total
failure rate was 4.3%. And the total failure rate for short implants was 3.6%. As shown
in table 9c, the failure rates of implants with lengths of 8, 10, 11.5, 13, and 16 mm were
0%, 3.8%, 0%, 4.7%, and 14.3%, respectively. This result was similar to result by Sun
HL (2011). Table 9d showed the failure rates of implants with diameter of 3.5, 4.3, and
5.0 mm were 2.0%, 6.9%, and 0%, respectively. According to Morand and Irinalis
(2007), the implant’s diameter and extension should be taken into account,
concomitantly, due to their interactive effects; the diameter is the most influent factor.
The log of the probability for failure was modeled as a function of age, implant length,
and implant diameter using a log-binomial (generalized) mixed-effects model with a
random intercept to account for the nested implants within subjects. Table 11 showed
the relative risk for failing as a function of implant length was low and not statistically
significant (p = 0.56). Relative risks for failing as a function of implant diameter and age
were also not significant (p = 0.45 for diameter, p = 0.32 for age). Figure 10 showed the
49
failure plots for age, implant length, and implant diameter. Where possible, a smoothing
spline (red line) was fitted to the observed failures. Failures were slightly “jittered” to
help show multiple points at the same location on the graph. In addition, the log-
binomial model predictions are shown (green lines). For each prediction curve, the other
explanatory variables were fixed to their respective means. These probabilities for
failure were estimated to be very small in addition to not being statistically significant. A
2009 retrospective study by Grant involved 335 implants 8mm in length placed in the
posterior mandible in 124 patients (median age 56 years, 112 partially edentulous)
between May 2005 and June 2007. The majority received fixed prostheses, while the
remaining received individual restorations. Four implants (in two patients) failed to
osseointegrate, and one implant fractured. Of the remaining 330, for up to two years
post-placement, the survival rate was 99%. The investigators concluded that the
placement of short implants was predictable and a suitable treatment for patients with
reduced bone height in the posterior mandible.
All implants in this study received single-unit fixed restorations or multi-unit fixed
bridge restorations and were placed in the premolar region. Data on the mean bone loss
at the restored implant are also presented. The results of this retrospective research
reveal that a statistically significant relationship did not exist between crestal bone loss
and implant length. These results compare favorably with retrospective analysis of
results from 247 dental implants with fixed prosthetics (crowns and bridges) by Draenert
in 2011. The relative risk for failing implant length was not significant (p = 0.57). Also the
relative risk for diameter and age were not significant (p = 0.45 and 0.32).
50
For several researchers (Gentile 2005; Morand 2007), bone quality is a
significant risk factor for failures due to lack of blood irrigation, overheating during
implant drilling in dense bones, and lack of bone density in trabeculated bone.
Goodacre (2003) considered that implants placed in poor bone quality areas showed
failures rates 16% higher than those placed into greater bone density areas. One way of
compensating the lack of bone quality would be to employ different techniques of
implant surface treatment and machining. Although the results of this study showed no
significant effects from age, implant length, or implant width on success, this remains a
retrospective study. The topic needs well-organized prospective research looking at
large sample sizes to confirm these results.
Short implants present a good alternative at posterior areas when the surgeon-
operator is in close proximity to the sinus or the mandibular canal. But superior clinical
judgment remains the key for successful implant treatment.
51
4.0 CONCLUSIONS
We concluded that short dental implants can be used in both jaws and could provide
acceptable alternative treatment for rehabilitation of areas with deficient alveolar bone
height or in areas in close proximity to the sinus, to avoid the necessity of lifting the
sinus. According to the mixed-effects-model point estimates for the slopes, a 1mm
increase in diameter is expected to decrease the square root of mean bone loss by
0.0965 √mm and 1mm increase in length is expected to increase the square root of
mean bone loss by 0.000511 √mm. These effects were not statistically significant,
although even if they were real, the estimated effects were small. As diameter
increased, mean bone loss was expected to decrease from 1.15mm to 0.86mm as the
diameter goes from 3.5mm to 5mm. And mean bone loss is expected to increase from
1.046 mm to 1.054 mm as implant length increases from 8 mm to 16 mm. This
negligible change was not statistically significant. A larger study would be needed to
better estimate the effects of implant length and diameter, but based on the data in this
study, the effects appear to be small at best.
The relative risk for implant failure for each 1 mm of length was estimated to be
1.17 (95% confidence interval: 0.69 to 1.99) but was not statistically significant (p =
0.57). Based on the confidence interval, the relative risk is poorly estimated and the
direction of the true effect is uncertain. The relative risk for implant failure for each 1mm
of implant diameter was estimated to be 2.86 (95% confidence interval: 0.19 to 42.6)
and was not statistically significant (p = 0.45). As indicated by the width of the
52
uncertainty in this estimate is huge and thus inconclusive as to the real risk. A one year
increase in age was estimated to increase the relative risk by 7% (1.07 with 95%
confidence interval: 0.94 to 1.21) and was not statistically significant (p = 0.23). It is
clear a larger study with many more subjects and implants, is needed to establish more
precisely the true relative risks for implant failure.
53
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